This invention relates to electronic publishing and particularly to defining and depicting colors for use in electronic publishing.
Electronic publishing has become the standard for developing documents for publication. Publication in this day and age includes not only printed publication but multi-media publications such as CD-ROM or World Wide Web documents as well. Thus, electronic publishing includes content preparation, such as text articles, images and even audio or video in multi-media documents, pre-press layout, proofing and printing.
Color is an important feature in designing documents for publication, whether for print or electronic publication. There are a number of concerns with the integration of color into electronic publishing, not the least of which is the accurate depiction of color on a computer monitor during the design and layout of the document relative to the final printed version. This concern is dependent upon a number of factors, including the spectral qualities relating to how the colors are displayed on a computer monitor screen as compared to the printed colors.
Another concern with color in electronic publishing is the limitations on the definition of colors. Presently, colors must be defined in terms of the components of a single traditional color model. Colors may be converted between these traditional color models, but may not be defined from more than one color model at a time.
A number of traditional color models are currently used in electronic publishing, depending on the document to be created and the printing process to be used. These color models normally fall into two categories, xe2x80x9cspotxe2x80x9d colors and xe2x80x9cprocessxe2x80x9d colors. Spot colors require a separate plate, that is, an image of a page, for each spot color used in the document. Spot colors are typically used for documents that only use one to three colors or for documents using special colors such as fluorescent colors, metallic colors or proprietary colors, such as a company color. Thus, spot colors are normally used for simple documents or for special colors.
Process colors are colors which are created by using percentages of primary color components, such as tints of cyan, magenta, yellow, and black (CMYK) that are blended together to create other colors. Process colors provide many more colors than spot colors for printing purposes and are normally used with documents containing color photography or other items using more than three colors. A document using process colors is separated into separate plates, each containing one of the component colors, such as four separate plates containing differing tints of four primary colors (CMYK). The process of splitting a composite document into its constituent plates and generating an image for each plate is called xe2x80x9cseparationxe2x80x9d.
One of the problems occurring with existing electronic publishing systems occurs when a document is created using process colors, but also requiring a spot color as well. For instance, a special color such as a fluorescent color or a metallic color may be used which can not be created using the process colors. Many documents may also require proprietary colors, such as in a company logo. For instance, a magazine having photography and a company logo may require both color models. Also, many high end publications may use a xe2x80x9cvarnishxe2x80x9d or other special color layer to be applied over an image to create an added effect. A xe2x80x9cvarnishxe2x80x9d may be a translucent color which tints an overall image or document to add a surface effect on the printed image. The addition of spot colors to a document using process colors is not a problem for the actual printing process. An additional plate is created for that particular spot color during the separation.
However, the adding of a spot color onto a document process color is a problem during the electronic design process. Presently, when such a spot color is applied during the design or layout phase of the publishing process, it is difficult to accurately depict on screen. Typically, during the design phase, the process document colors are converted to a color model which can be depicted on a computer monitor screen, such as RGB or LAB. However, the existing algorithms are unable to convert process colors which have been combined with spot colors or with the combination of arbitrary inks. If an on-screen image using process colors is overlayed by the spot color, then that image is blocked from view. Typically, the designer will create two duplicate boxes, one containing the image and the other containing the spot color to be applied. The final image to be printed is not able to be accurately displayed prior to the actual printing of the image. This is of concern since neither the designer nor others later working with the document are sure of the final image.
Since process colors are normally used in most higher end documents, this is an important issue in the publishing industry. Thus, a problem exists in accurately depicting color documents during the electronic design of such documents.
Another problem with the prior electronic publishing systems is the definition of colors digitally. The prior electronic publishing systems utilize standard color models to define colors used in the document and the depiction of the document on a computer screen. These standard color models, such as RGB, LAB, CMYK, Hexachrome, Pantone and others, each use defined color components. For instance, a color defined in the RGB color model uses differing percentages of Red, Green and Blue, the color components of the RGB color model. A color defined in the CMYK color model only uses percentages of Cyan, Magenta, Yellow and/or Black. A color defined in the Hexachrome color model only uses percentages of Cyan, Magenta, Yellow, Black, Orange and Green. Each of the color models use only their respective components in defining a color.
These electronic publishing systems are unable to define a color using xe2x80x9carbitraryxe2x80x9d color components. These color components, often referred to as xe2x80x9cinksxe2x80x9d, are limited for use only within their respective color model. Colors defined in terms of inks in one color model may be converted into the inks of another color model, but a color has not been able to be previously digitally defined in the inks of more than one color model at a time. Thus, a problem exists in the inability to define a color with color components or inks outside of a particular color model.
The present invention solves these and other problems by providing a process and system for defining and representing combinations of colors that was not previously possible. In accordance with one preferred embodiment of the present invention, the process includes a user-definable xe2x80x9cmeta-inkxe2x80x9d color which is made up of the components of the process colors and the spot colors and the shade values assigned to each of the color components. The document color is then replaced by this meta-ink color for depiction purposes on a radiant light source, such as a computer monitor screen.
This process is implemented, in one preferred embodiment, by a model wherein the meta-ink colors are defined as a series of references between document colors (a named entity which describes a color in a document). These references each specify the meta-ink color, the spot or process color and the percentage (or shade) of each meta-ink color on the spot or process color or even on an arbitrary color, as defined in greater detail in the discussion of a preferred embodiment. Any number of meta-ink colors may be attached to any number of colors.
The system of the present invention, in one preferred embodiment, takes the user-defined meta-ink color and converts the process color components and their assigned shade values of this meta-ink color into RGB values. The system then shades each of the RGB components of the spot colors of this meta-ink color according to the shade values which have been assigned to each of the components in the definition of the meta-ink color. The shaded values for each of the spot color components is xe2x80x9clayeredxe2x80x9d onto the RGB values converted from the process color components of the meta-ink color in an iterative process. That is, each of the spot colors defined in the meta-ink color are respectively layered onto the preceding value of the previously defined spot color layered onto the RGB values converted from the process color components. The final value of the iterative process is computed and converted into a color model suitable for the radiant light source, such as a LAB color model value. This process essentially treats the color inks as a series of photographic filters which attenuate the spectrum of the combined colors to depict the combined colors in an accurate representation of the printed image. This layering of the spot colors is analogous to placing a series of photographic filters, one for each spot color, over the image. The spot colors are thus able to be more accurately depicted on the screen as a match for the colors of the printed image.
These and other features of the present invention are described in greater detail in the ensuing description of a preferred embodiment and in the drawings.